1. Field of the Invention
The present invention relates to an image falsification detection device and an image falsification detection method. More particularly, the present invention relates to an image falsification detection device and an image falsification detection method in which, when an original document of interest is produced, falsification detection information reflecting its content is incorporated thereinto, and in which whether or not a read image is falsified is detected by use of the falsification detection information.
2. Description of the Related Art
An original paper document falsification detection technology is becoming important as there has been growing security awareness in recent years (see, for example, a catalog for “Guardian of Paper”, security software for printed document, published by Hitachi Government & Public Corporation System Engineering, Ltd. in February 2009). In this technology, an image of interest is first converted into a lower resolution image, the low-resolution image is converted into a barcode, and the original image (the image before being converted into the low-resolution image) and the barcode are printed on paper. Then, the following processing is performed to check whether or not the content of the printed paper is falsified. The paper (also referred to as an original paper document) is scanned, and thus the density of the image within the barcode is compared with that of the image obtained by the scanning. As a result, if, in a certain region, there is a density difference between those images which is equal to or more than a threshold value, the region is determined to be a falsification detection region. For example, the region is determined to be a region in which a person has put information into the above paper in handwriting or has erased part of the image in the region with a correction pen or the like.
However, in the related art of above “Guardian of Paper”, in order to appropriately set the threshold value, it is necessary for a user to manually perform adjustment. This imposes a burden on the user.
An object of the present invention is to determine appropriate threshold values for detecting falsification in various original paper documents. For example, the present invention has an object to determine a threshold value for appropriately detecting falsification in an original paper document even when an image in the original paper document is degraded because, for example, the original paper document has been left for a long period of time.